Optical devices

Abstract

A solid-state, surface-emitting, optical device such as a light emitting diode (LED) or vertical cavity surface emitting laser (VCSEL) has a body of optical gain medium overlying a high reflectivity distributed BRAGG reflector (DBR) mirror which is carried on part of an underlayer. The gain layer is part of an epitaxial layered structure extending from the underlayer and over the mirror.

1 . A solid state, surface-emitting, optical device having a body of optical gain medium overlying a high reflectivity distributed Bragg reflector (DBR) mirror which is carried by an underlayer, 
 wherein the mirror is a multi-layer dielectric fabrication having alternate layers of dielectric material with a high refractive index ratio between the adjacent layers in the fabrication, and the body of optical gain medium is part of an epitaxial layered structure extending from the underlayer and over the fabrication.    
     
     
         2 . A device as claimed in  claim 1 , wherein the high refractive index ratio is greater than 1.3.  
     
     
         3 . A device as claimed in either preceding claim, wherein the underlayer comprises a substrate having a buffer layer which is a nitride of a group three element in the periodic table.  
     
     
         4 . A device as claimed in any preceding claim, wherein the epitaxial structure is formed by combinations from the InAlGaN quaternary system.  
     
     
         5 . A device as claimed in  claim 4 , wherein the epitaxial structure includes an Indium Gallium Nitride-based (InGaN) multi-quantum well structure.  
     
     
         6 . A device as claimed in any preceding claim, wherein a further mirror which is partially optically transmissive is disposed on the epitaxial structure in registration with the DBR mirror so that the epitaxial structure functions as a solid stare optical cavity.  
     
     
         7 . A method of fabricating a solid-state, surface-emitting, optical device incorporating an improved distributed Bragg reflector (DBR) mirror, the method comprising the steps of: 
 providing an underlayer;    growing a multi-layer coating on the underlayer, the coating comprising alternate layers of high refractive index dielectric and low refractive index dielectric;    selectively removing portions of the coating to provide an array of free-standing dielectric fabrications whereby portions of the underlayer are revealed between adjacent fabrications;    epitaxially growing a semiconductor layered structure incorporating a body of optical gain medium on the revealed portions of the underlayer so that a lower part of the structure grows up and laterally on top of the free-standing dielectric fabrications, and an upper part of the structure incorporates the body of optical gain medium and overlies the fabrications so that one of the free-standing fabrications provides the DBR mirror.    
     
     
         8 . A method as claimed in  claim 7 , comprising the steps of growing a further mirror on the body of optical gain medium; 
 providing a first electrode electrically connected to one side of the optical gain medium in registration with said one of the free-standing fabrications; and    providing a second electrode electrically connected to the opposite side of the optical gain medium;    so that the optical gain medium functions as an optical cavity which may be electrically activated by the electrodes.    
     
     
         9 . A method of fabricating a solid-state surface-emitting optical device incorporating an improved distributed Bragg reflector (DBR) mirror, the method comprising the steps of; 
 providing an underlayer;    selectively patterning a surface of the underlayer to provide an array of depressions in the surface;    providing an array of dielectric fabrications in the depressions with portions of the underlayer revealed between adjacent fabrications, each fabrication comprising alternate layers of high refractive index dielectric and low refractive index dielectric;    epitaxially growing a semiconductor layered structure incorporating a body of optical gain medium on the revealed portions of the underlayer so that a lower part of the structure grows up and laterally on top of the free-standing dielectric fabrications, and an upper part of the structure incorporates the body of optical gain medium and overlies the fabrications so that one of the free-standing fabrications provides the DBR mirror.    
     
     
         10 . A method of fabricating a solid-state surface-emitting optical device incorporating an improved distributed Bragg-reflector (DBR) mirror, the method comprising the steps of: 
 providing an underlayer of gallium nitride;    patterning the underlayer with laser-drilled holes;    epitaxially growing a semi-conductor layered structure incorporating a body of optical gain medium on a surface of the underlayer so that the lower part of the structure grows up and laterally on the surface and overlies the holes therein; and    fabricating a multi-layer coating within the thickness of the holes so that the fabrications are carried by both the underlayer and the epitaxial layered structure overlying the holes.